Now I am doing my DBA research, the whole population are the public university teachers in one of Chinese 's province, there are 22 universities. and I want 400 samplings, the total population is 26400, Can I sample the number of teachers in each university in proportion? for example, A university has 2000 teachers, B university has 1500 teachers, C university has 1000 teachers, so I sample A university 20 ,B 15, C 10 ,teachers to answer questionnaire. Is that ok if I use this sample design? is that called stratified random sampling? If I can't use this design, what should I do?
thank you very much!!!
Yes, yours is called stratified. I am not very experienced in probability sampling methods, but you should consider several factors:
(1) How much will the results from each university vary? Would they vary a lot, you will find it harder to conclude from the data collected.
(2) It also depends on the type of data (binary, continuous..) that you received. This is basic statistics, as it will require a larger sample for better estimations of your desired conclusion.
(3) About the decision of proportionate or disproportionate sampling (as you suggest, it is proportionate), this depends on the way you aggregate your data (is there any weight or adjusted factor for each university, or they are considered as equal regarding your research), units of observation are the teachers, and units of analysis are the universities, or else... I would suggest proportionate sampling (your suggestion).
(4) Limitation of the sample size. What is the min number of survey do you need to achieve statistical significance. What is the factor constraint your upper limit.
Hello Yao Tang,
What you have described is only one layer or strata in a stratified random sampling. To achieve a higher degree of "randomness" you will probably need other stratas, such as (2) gender, (3) number of professor in different departments.
I will suggest at least 3 strata to do stratified sampling. Too many also makes the selection very difficult.
Kind regards
Prof Adrian Kuah
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